This invention relates to the findings of multiple circulation frequency operation and broadband operation with various ferrite-composite Y circulators, and improvement and miniaturization of stripline junction circulators, such as Y-junction circulator, X-junction circulator and other multiple-port junction circulators.
The basic stripline Y-junction circulator comprises a pair of ferrite structures, a stripline Y-junction having three stripline branches symmterically extending away from a common region with the same size as that of the ferrite structures attached, and two ground planes covering the device. The biasing magnetic field is applied parallel to a common axis of the ferrite structures.
According to the invention, the ferrite structure acting as nonreciprocal element in the stripline Y circulator is replaced by various ferrite-composite structures. There are three types of ferrite-composite structures, i.e., a ferrite-conductor composite (F/C composite), a ferrite-dielectric-conductor composite (F/D/C composite) and a ferrite-ferrite composite (F/F composite). These ferrite composite structures are made in such a way that constituent elements of a ferrite composite structure are combined, one outside of the other, in the radial direction, to have the last ferrite layer externally encircling the internal portion of the composite.
The electromagnetic fields of the transverse magnetic field mode (the TM mode) are important in these ferrite composite structure, and also in a stripline Y-junction circulator. In the circulator, a ferrite composite structure acts as a coupled resonator through the stripline Y-junction so that resonant TM modes proper to the ferrite composite are coupled one with the other. The circulator action can be, therefore, described in terms of resonant TM modes and coupled TM modes, or rather circulating modes. Generally speaking, circulator action can be represented by circulations at operating points for perfect circulation as has been mentioned in my aforesaid U.S. Pat. No. 4,122,418. The ferrite composite circulators of the invention provide new facets of circulator performances which are represented by multiple circulation frequency operation and its developments, by achieving circulations at two or more operating points of perfect circulation, thus disclosing the way of multiple operating point circulation.
As known in the art of circulators, there are disclosed various types of improved circulators in embodiments of U.S. Pat. Nos. 3,350,663, 3,714,608, 3,851,279, 3,422,375, 3,350,664, and 3,355,679. These prior art circulators commonly utilize the lowest order circulation which consists of the lowest order TM mode among various resonant modes of the ferrite structure, following the way of single operating point performance. Dimensions of a ferrite structure and biasing magnetic field intensity in the design of the prior art circulator closely depend on the lowest-order circulation but not on any other circulations.
One of the prior art circulators accounts for a different version in the way of multiple operating point performance, in that multiple resonances are utilized to get a broadband. It is disclosed in the embodiments of U.S. Pat. No. 3,714,608 (Barnes et al, "Broadband circulator having multiple resonance modes") that the lowest-order circulation having additionally various order resonances in the axial wave propagation produces broadband performance, by introducing multiple resonances so spaced in the frequency spectrum as to get desirable characteristics over a broadband. This art of broadbanding, however, belongs to the category of a single operating point performance from the viewpoint of multiple operating point performance using multiple resonant modes of the radial wave propagation. Insofar as a single operating point performance is used, a narrow band circulator is obtained. Broadbanding of a circulator has long been widely achieved by connecting a broadbanding transformer for impedance matching at each port of the Y-junction. It is effective to get a broadband circulator. However, the gross dimensions of the device become large and symmetric impedance adjustments inevitably result in cost increase. Besides, the design principle of the prior art circulator is not favorable to microwave integrated circuit technology (MIC).
As briefly above-mentioned, the basic principle of circulator action in the circulator of the invention is entirely different from the design principle adopted in the above-described prior art circulators. In the embodiments of the invention, many resonant modes and so many circulating modes, which have been disregarded in the prior art circulators, are positively utilized. Further close discussion on comparison between the prior art circulators and embodiments of the invention will follow after the objects of the present invention is clarified.
An object of the invention is to provide an improved circulator performance, such as broadband operation and variable broadband performance.
A further object of the invention is to provide a new circulator performance, such as diplexer operation or frequency dividing operation.
A still further object of the invention is to provide a ferrite composite circulator of reduced size and weight, favorable to MIC.
Three types of ferrite composites used, i.e., F/C composite, F/D/C composite, and F/F composite, and embodiments of the invention will now be compared in detail with the prior art circulators.
The F/C composite circulator of the invention and the prior art circulators are compared as follows.
(1) Regarding U.S. Pat. No. 3,350,663 (Siekanowicz et al, "Latched ferrite circulator"), it disclosed the ferrite-dielectric-ferrite-conductor combination (the F-D-F-C combination) in the centripetal way in the radial direction in the latched ferrite circulator given in FIG. 6 of their drawings in the above-cited patent. Let the dielectric layer holding the conducting loop be negligibly thin enough as is disclosed, and then the F-D-F-C combination becomes the F-F-C combination which plays a major active role in this latched ferrite circulator. In order to acquire the return path for the magnetic flux flow, two ferrite portions in the F-F-C combination have inversed magnetizations so that clockwise and counter-clockwise rotating field waves of one ferrite do not connect with respective rotating field waves of the other but inverse rotating field waves. Consequently, the totally resonant field modes in the F-F-C combination of the latched ferrite circulator are completely different from those of the F/C composite of the invention. If the dielectric layer is taken into account, the resonant field modes in the F-D-F-C combination become much complicate in comparison with those of the F/C composite. Accordingly, circulating modes and circulations in the latched ferrite circulator will have definitely different characteristics.
(2) Regarding U.S. Pat. No. 3,714,608 (Barnes et al, "Broadband circulator having multiple resonance modes"), it disclosed the ferrite-dielectric-conductor combination (the F-D-C combination) in the centripetal way in the transverse section as an active element in the embodiments given in FIGS. 1, 3, 4, 5, 6, and 8 of their drawings. The most important is that no matter how thick the dielectric layer between the ferrite cylinder and conductive pin may be, and no matter how thick the conductive pin may be, the structure of the F-D-C combination acts as a wave-transmission-line resonator in the axial direction. The active element is designed to support the axial wave propagation having the lowest resonance in the radial direction, from which the broadbanding effect is induced. Contrarily, the F/C composite of the invention is too thin to support any resonance of such axial wave propagation, and the composite does not produce any axial wave propagation.
(3) U.S. Pat. No. 3,851,279 (Andrikian, "Tee junction Waveguide circulator having dielectric matching posts at junction") disclosed the ferrite-dielectric-conductor combination (F-D-C combination) in the axial direction of the device. The combination of this kind does not influence resonant characteristics of the TM modes, because the TM mode is only determined by the condition of a magnetically short-circuited edge (the magnetic wall) at the periphery of the ferrite portion. Dielectric and conductor portions play different roles in circulator adjustments, particularly in impedance matching. The conductive platform has a role to decrease the junction impedance of the waveguide junction, and the dielectric layer has a role to match the intrinsic wave impedance of the ferrite to the waveguide impedance. After all, each of them acts as one of impedance matching transformers.
(4) U.S. Pat. No. 3,422,375 (Omori, "Microwave power dividing network") disclosed a embodiment of a microwave power divider which consisted of a stripline X-junction having a circular common region larger than the radius of the ferrite structure, and a pair of the same F/C composite of the present invention. It is marked that the power divider operates at the intersection of resonant mode curves TM.sub.010 (n=0.1) and TM.sub.110.sup.- (n=-1) in the region below resonance, or could operate at the intersection of resonant mode curves TM.sub.010 (n=0.1) and TM.sub.110.sup.+ (n=+1) in the region above resonance, where numbers in parentheses denote the notations of modes given by Bosma ("On stripline Y-circulation in UHF," IEEE Trans. on Microwave Theory and Tech., vol. MTT-12, pp. 61-72, January 1964; FIG. 4, p. 67). The operating region shown in FIG. 2 of their drawings apparently indicates the operation below resonance. The operating range of the power divider is considered to be in the resonant mode curves given by the relation of radial wave propagation constant-radius product k.sub.e r.sub.0 versus ferrite anisotropic splitting factor .kappa./.mu. the range where resonant mode curves n=0.1, +1, +2, and others of positive orders get together at the point of k.sub.e r.sub.0 =0 and .kappa./.mu.=1.0 in the region above resonance, and contrarily, where resonant curves n=0.1, -1, -2, and others of negative orders get together at the point of k.sub.e r.sub.0 =0 and .vertline..kappa./.mu..vertline.=1.0, as shown in FIG. 3 of the drawings of the present invention. Furthermore, the operating range is easily identified in the mode chart which is given by the relationship of biasing magnetic field intensity and frequency as schematically shown in FIG. 4 of the drawings of the invention. It is found that the operating range above resonance is located at the lowest biasing magnetic field intensity in the lowest frequencies in the neighborhood of ferromagnetic resonance absorption in the region above resonance, while the operating range below resonance is located at the lowest frequency of the resonant mode n=-1, with such a specific intensity of biasing magnetic field that the specific effective permeability of the ferrite .mu..sub.e becomes zero and the anisotropic splitting factor .kappa./.mu. becomes negative unity, which is derived from Polder's equations of tensor permeability of the ferrite (Polder, "On the theory of ferromagnetic resonance," Phil. Mag., vol. 40, pp. 99-115, January 1949). Consequently, the radial wave propagation constant k.sub.e at the operating range is almost nearly zero, and becomes imaginary if the ferrite structure is biased magnetically exceeding the operating range, as the electromagnetic field energy dissipating. Anyway, the operating range is adjusted in such way.
However, with the specific biasing magnetic field intensity pertaining to the operating range below resonance, other higher-order resonant modes taking place in higher frequencies as seen in FIG. 4 of the invention will come into the operation of the power dividing even if these modes are out of resonance, thereby the desirable power dividing operation deteriorating. To secure the power dividing operation, the stripline X-junction, with such large common region as to have its rim exceed the diameter of the ferrite structure, acts to make the two resonant modes, TM.sub.010 and TM.sub.110.sup.-, dominate and to suppress other higher-order resonant modes. With this oversized common region of the X-junction, the TM.sub.010 mode is enforced to have the em fields equal to those of the TM.sub.110.sup.- mode, so as to produce a power dividing operation.
In other words, as is disclosed in Column 3, line 16 in the cited patent, "the diameter of post 20 should have such a ratio to the diameter of the common portion of spider 12 that the loaded Q's of the two modes are equal. With equal Q's, power applied to any of the ports will divide equally between the TM.sub.110.sup.- and TM.sub.010 modes." However, though it says in Column 2, lines 56 that post 20 has a diameter that is in the order of three tenths to six tenths of the diameter of the common portion of spider 12, the ratio of the diameter of the common portion of spider and the diameter of the ferrite structure, besides the ratio of the diameter of the common portion of spider and the diameter of the conductive post, should have importance. The former ratio for the ferrite structure is not clearly mentioned. Insofar as the power divider is concerned, the stripline X-junction having an oversized common region is used. Thus, the common region of the X-junction in conjunction with the conductive post of the F/C composite has a unique effect on the power dividing operation in the Omori's way of operation.
As for a stripline X-junction circulator, for the sake of comparison, it consists of a stripline X-junction and a pair of F/C composites loaded therein. The stripline X-junction is designed to have a common region of the same diameter as that of the F/C composite. If the X-junction has an oversized common region, not only the lowest-order circulation but also higher-order circulations will be deteriorated and merely a power dividing operation will take place. As to the X circulator, a stripline X-junction having a common region of the same size as a F/C composite is therefore effective to perform multiple circulation frequency operation.
The F/D/C composite circulator of the invention and the prior art circulators are compared as follows.
(1) U.S. Pat. No. 3,350,663 (Siekanowicz et al, "Latched ferrite circulators") disclosed various combinations among ferrite, dielectric, and conductor in the embodiments of the latched ferrite circulator as shown in FIGS. 6, 11, and 13 of their drawings. The embodiments disclosed in the FIGS. 6 and 11 give the examples of the ferrite-dielectric-ferrite-conductor combination (F-D-F-C combination) and the ferrite-dielectric-ferrite-dielectric-conductor combination (F-D-F-D-C combination), respectively, in the radial direction. Essential distinctions which they bear are that each ferrite element in both embodiments of the FIGS. 6 and 11 has inverse magnetization to produce the return path for the biasing magnetic flux flow, thereby inversely connected opposite rotating em fields producing unique resonant field modes and their circulating modes completely differing from those of the invention as early mentioned.
The embodiment illustrated in the FIG. 13 discloses the F-D-C combination in the radial direction which closely resembles the F/D/C composite of the invention. The latched ferrite circulator disclosed in the FIG. 13 is such that iron post 76, iron disk 77, 78 amd ferrite ring 79 produce the return path for magnetizing flux flow; the conducting turn as the magnetizing current loop is positioned in the dielectric; each ferrite and iron assembly, consisting of a ferrite element, iron pieces for the flux return path and the conducting turn, is separated by dielectric spacers from the conductor of the common region of the X- or Y-junction, and two ground planes.
Insofar as the F-D-C combination in the latched ferrite circulator is concerned, resonant field modes of the TM type may be all the same as those of F/D/C composite if inhomogeneous magnetization probably caused by such insufficient magnetizing system used is neglected, and if the influence of the conducting turn is also disregarded.
The F-D-C combined structure, however, is electrically short-circuited at the upper and lower planes by so many severed iron pieces that the em fields inside the F-D-C combined structure will be modified by these sectoral iron pieces which produce resonant characteristics depending on an angle of the sector iron and a gap between two sectors in the angular direction. In the embodiments disclosed in the FIG. 13, the X- or Y-junction are loaded by a pair of the F-D-C combined structures short-circuited with the iron pieces, whether the iron pieces are severed or not. In any case, incident waves at the X- or Y-junction will be divided into two resonators. The one is for the dielectric separators 82, 83, 82', and 83' bounded by iron disks 77, 78, 77', and 78', and conductors of a common region and upper and lower planes of the junction. The other is for the F-D-C combined structure bounded by iron disks 77, 78, 77', and 78'. To achieve perfect circulation with the embodiment consisting of the two resonators, coupling effect between them must be taken into account. The F/D/C composite circulator of the invention does not have any complexity that the latched ferrite circulator bears.
(2) U.S. Pat. No. 3,714,608 (Barnes et al, "Broadband circulator having multiple resonance modes") disclosed the embodiments having the F-D-C combined structures. As early mentioned, the F-D-C combination consists of a ferrite cylinder which has a small hole, a thin spacer, and a conductive thin pin. Each F-D-C combined structure provides a different electrical path length for each counter rotating mode of the lowest order, as counter rotating modes propagate along the F-D-C combination in the axial direction. In a further embodiment, a thin conductive pin is located axially in each ferrite cylinder, which has a different axial length to provide double resonances. According to the disclosure of the cited patent, the active element is designed to support the axial wave propagation having the common lowest-order resonance defined in the radial direction.
The broadbanding is effected by introducing multiple axial resonances so spaced in the frequency spectrum from each other that the characteristics of reflection coefficients versus frequency (or scattering eigenvalues versus frequency) merge to form a continuum of constant slope across the broadband. Provided that the second-order resonance defined in the radial direction is additionally introduced, whether or not the second group of multiple axial resonances can merge to form another constant slope continuum across the broadband is a new problem that is apparently beyond the disclosure of the cited patent.
Contrarily, the F/D/C composite of the invention does not provide any resonance coming from the axial wave propagation and is too thin to support any of such axial wave propagation. Only the resonant modes of the TM type produced in the transverse directions are utilized in the F/D/C composite circulator of the invention.
(3) U.S. Pat. No. 3,851,279 (Andrikian, "Tee junction waveguide circulator having dielectric matching posts at junction") disclosed the F-D-C combination (which may be, strictly speaking, the C-D-F-D-C combiantion) in the axial direction, in which each element of the F-D-C combination is piled up. This combination, however, does not produce any other mode than the resonant TM modes specifically defined by the condition of the magnetic wall at the periphery of the triangular ferrite portion. Conductive and dielectric portions in the F-D-C combination produce impedance matching effect between the symmetric junction wave impedance of the junction and the intrinsic wave impedance of the ferrite portion. The Tee junction is unsymmetric so that it needs transformation for impedance matching between the symmetric ferrite combined structure and the unsymmetric Tee junction. The dielectric posts are used for that purpose. From these considerations and as is early mentioned, the F-D-C combination in the axial direction in the embodiment disclosed in the cited patent has the same resonant modes as the triangular ferrite has. Therefore, if a disk ferrite is compared to the triangular ferrite, the F/D/C composite has no counter part.
The F/F composite circulator of the invention and the prior art circulator are compared as follows.
(1) U.S. Pat. No. 3,350,663 (Siekanowicz et al, "Latched ferrite circulator") disclosed the F-F combination in the embodiments of the latched ferrite circulator. As is disclosed in the embodiment, it says that all ferrite elements may be of the same ferrite or they may be of different ferrites, in order to provide the return path for the magnetic flux flow, with the cross section area adjusted for continuity of the flux flow. The F-F combination in the latched ferrite circulator is considered to retain a common feature with the different ferrite structure in which a set of different ferrites is incorporated for the ferrite elements in the F-F combination. Each ferrite element is separated by a dielectric holding a magnetizing loop in the F-F combination. A ferrite element inside the dielectric is magnetized inverse to the one outside it for the purpose of the flux return path. Therefore, clockwise and counterclockwise rotating fields in one ferrite element inversely connect with counterclockwise and clockwise rotating fields in the other element. Contrarily, the F/F composite is unidirectionally magnetized so that opposite rotating fields in one ferrite element are connected correspondingly to those in the other ferrite element. Consequently, the F-F combination in the latched ferrite circulator has a role for a flux return path that the F/F composite does not necessitate, and definitely different resonant modal characteristics from those of the F/F composite. These comparisions lead to a conclusion that the latched ferrite circulator is completely different from the F/F composite circulator.